Learn Hardcore Czech: Na dnešní večírek si vezmu modré kalhoty a černé boty. - For tonight's party I will put on blue trousers and black shoes.

na + accusative is used for:
- events / activities: na koncert, na večírek, na schůzku, na dovolenou
- surfaces / open areas: na stůl (onto the table), na náměstí (to the square)
do + genitive is used for:
- closed spaces / interiors: do školy (to school – the building), do kanceláře (to the office), do města (to the city - going into it)

A večírek is an event/party, so Czech uses na večírek (“to the party”).
Do večírku would sound wrong in this sense.

What case is dnešní večírek, and how can I tell?

In na dnešní večírek, the phrase dnešní večírek is in the accusative singular.

The preposition na here means “to (an event)” and it requires the accusative.
Večírek is masculine inanimate. For masculine inanimate nouns, nominative and accusative are usually the same form:
- Nominative: več írek
- Accusative: več írek (no change in form)

Because of the preposition na (with the “to an event” meaning), we know this must be accusative, even though it looks like nominative.

Dnešní is an adjective-like form and just stays as dnešní for all genders in singular nominative and accusative, so it doesn’t show the case change either.

What exactly does dnešní mean, and how is it related to dnes?

Dnes means “today”.
Dnešní is a derived adjective-like word meaning “today’s” or “of today”.

So:

dnes = today
dnešní večírek = today’s party, the party taking place today

You could translate the whole start as “For today’s party…”

Why do we say si vezmu instead of just vezmu? What does si add?

The verb here is vzít si (perfective) – literally “to take for oneself”, and very often it means “to put on / to wear” in contexts about clothing.

vezmu = “I will take (something)” (no reflexive)
vezmu si = “I will take (for myself) / I will put on / I’ll wear”

In this sentence:

Na dnešní večírek si vezmu modré kalhoty a černé boty.
→ “For today’s party I’ll wear blue trousers and black shoes.”

If you said only vezmu modré kalhoty, it would sound more like “I’ll take the blue trousers (along)” – e.g. pack them into a bag.
With si, the natural interpretation with clothes is “I’ll put them on / I’ll wear them.”

Why is the word order si vezmu, not vezmu si? Is si in a fixed position?

Si is a clitic – a short, unstressed pronoun that likes to stand in the second position in the clause.

Both of these are correct:

Na dnešní večírek si vezmu modré kalhoty a černé boty.
Na dnešní večírek vezmu si modré kalhoty a černé boty. (grammatically possible but sounds unnatural)

In natural Czech, clitics (like si, se, mi, ti, ho, by, jsem, jsi) almost always move towards the second slot in the sentence or clause. Here, Na dnešní večírek is the first chunk, and si slides right after it into second position:

[Na dnešní večírek] si vezmu …

So the word order si vezmu is driven by this “second position” rule, not by emphasis.

What tense is vezmu? Why doesn’t Czech use something like budu brát for the future?

Vezmu is the future tense of the perfective verb vzít (si).

In Czech:

Perfective verbs form the future using their present endings:
- vezmu = I will take
- koupím = I will buy
- napíšu = I will write
Imperfective verbs use budu + infinitive for the future:
- budu brát = I will be taking / I’ll take (repeatedly / habitually)
- budu kupovat, budu psát, etc.

Talking about a single planned action in the near future (what you’ll wear tonight), Czech prefers a perfective verb:

vezmu si kalhoty = I’ll put on trousers (once, specific event)

So si vezmu here is a simple future meaning “I’ll wear / I’ll put on”.

Why are kalhoty and boty plural in Czech, even though in English we say “trousers” (plural) but “a shoe” (singular)?

Czech treats both kalhoty (trousers) and boty (shoes) as plural nouns by default:

kalhoty – always plural: one pair of trousers is still grammatically plural
- Mám nové kalhoty. = I have new trousers.
boty – plural of bota (shoe). When you mean the usual pair of shoes, you normally use the plural:
- Mám nové boty. = I have new shoes.

In this sentence, you’re clearly talking about one pair of trousers and one pair of shoes, but Czech grammar still uses the plural form:

modré kalhoty – blue trousers (one pair)
černé boty – black shoes (one pair)

If you wanted to emphasize a single shoe (one, not a pair), you’d say jedna bota.

What case are modré kalhoty and černé boty, and how do the endings show that?

Both modré kalhoty and černé boty are in the accusative plural, because they are the direct objects of si vezmu.

Kalhoty: feminine plural noun
Boty: feminine plural noun

For hard-stem feminine plural nouns in the accusative, the noun ending is -y and the adjective ending is -é:

Nominative plural: modré kalhoty, černé boty
Accusative plural: modré kalhoty, černé boty (same forms)

So:

kalhoty – feminine plural, accusative = nominative
boty – feminine plural, accusative = nominative
modré, černé – feminine plural adjective endings in both nominative and accusative

The fact that they are objects of vezmu tells you functionally they’re accusative, even though the forms look identical to nominative.

Why do modré and černé both end in -é? Does that mean they’re the same gender and number?

Yes. In modré kalhoty and černé boty, the adjectives modré and černé both:

agree with a feminine plural noun
are in the nominative/accusative plural form

Adjective pattern (hard type modrý = “blue”):

Masculine animate plural accusative: modré (but with different context)
Feminine plural nominative/accusative: modré
Neuter plural nominative/accusative: modrá

Because kalhoty and boty are both feminine plural, you get:

modré kalhoty
černé boty

So yes, the -é ending here signals feminine plural (nom./acc.).

Could I change the order and say Na dnešní večírek si vezmu černé boty a modré kalhoty? Does it change the meaning?

You can absolutely change the order:

Na dnešní večírek si vezmu modré kalhoty a černé boty.
Na dnešní večírek si vezmu černé boty a modré kalhoty.

The basic meaning is the same: you’ll wear blue trousers and black shoes.

The only difference is a very slight focus: items mentioned earlier can sound a bit more prominent. But in everyday speech, people will not interpret any real change in meaning; both orders are normal.

Can I leave out si and say Na dnešní večírek vezmu modré kalhoty a černé boty?

You can say it grammatically, but the meaning shifts:

Na dnešní večírek si vezmu modré kalhoty a černé boty.
→ I’ll put on / wear blue trousers and black shoes to today’s party.
Na dnešní večírek vezmu modré kalhoty a černé boty.
→ I’ll take blue trousers and black shoes to today’s party (e.g. carry them there, bring them along in a bag), not necessarily wear them.

To express what you’ll wear, it’s much more natural to use vzít si (with si) in this context.

What’s the difference between večer and več írek? Both are translated with “evening” or “party” sometimes.

večer primarily means “evening” (the time of day). In some contexts it can also refer to a vague “evening event”.
- Dnes večer nejdu nikam. = I’m not going anywhere this evening.
več írek is a noun for an event: a party / small party / evening get-together – often a more informal social event.

So:

dnes večer = this evening (time)
dnešní večírek = today’s party (event)

In your sentence, več írek clearly means a party, not just “the evening”.

Where is the stress in dnešní večírek, and are there any pronunciation traps?

Stress in Czech is almost always on the first syllable of each word:

DNEŠ-ní – stress on DNEŠ
VE-čí-rek – stress on VE

Pronunciation tips:

The cluster dn in dnešní is really pronounced as [dn], not like in English “dinner”.
š = English “sh”
č = English “ch” in “church”
Long vowel í in dnešní and in the -í- of več írek is held longer.

So roughly: DNEŠ-nee VE-chi-rek (using English-ish approximation).

Could I use budu mít na sobě instead of si vezmu to talk about clothes?

Yes, that’s another very common way to talk about what you’ll be wearing:

Na dnešní večírek si vezmu modré kalhoty a černé boty.
Na dnešní večírek budu mít na sobě modré kalhoty a černé boty.

Both mean basically: “For today’s party I’ll be wearing blue trousers and black shoes.”

Nuance:

si vezmu – focuses on the act of putting them on (what you’ll choose to wear / take for yourself to wear).
budu mít na sobě – focuses slightly more on the state of having them on, i.e. how you’ll be dressed.

In everyday speech, both are very natural and often interchangeable.